1. Field of the Invention
This invention relates to a packaging material for photosensitive materials, suitable for packaging relatively heavy products including various photographic photosensitive materials, other photosensitive materials and electronic parts, such as rolls of film for movies.
2. Description of the Prior Art
In general, packaging materials for the products of high technology, such as photographic photosensitive materials, are required to satisfy various properties, such as gas barrier, moistureproofness, physical strength such as breaking strength, tear strength, impact puncture strength, Gelbo test strength and wear resistance, heat sealing properties such as heat seal strength, side welding properties, hot tack properties and sealability with other materials, antistatic properties, slip properties, low dusting, and flatness, in addition to the light-shielding ability capable of shielding light completely.
Heretofore, various proposals have been made for satisfying the above properties.
The inventor has conducted investigations for improving the packaging materials for photosensitive materials, and for example, he has disclosed a packaging material wherein the physical strength is improved by combining two uniaxially stretched films (U.S. Pat. No. 4,331,725). The inventor has also disclosed a laminated film, composed of a foamed sheet having a thickness of 0.3 to 2 mm and a blow-up ratio of 5 to 50 times and two uniaxially molecularly oriented thermoplastic resin films adhered on the both sides of the foamed sheet by melt adhesion directly or through an extrusion laminating adhesive layer so that respective molecular orientation axes cross each other at an angle of more than 30 degrees, of which the thickness is reduced to 40 to 85% of the total thickness by pressing (U.S. Pat. No. 4,565,733). The laminated film has a great impact puncture strength and Gelbo test strength, and it is excellent as a packaging material for heavy products.
However, the above packaging materials were inferior in the dispersibility of carbon black, and lumps and fish eyes frequently occurred. They were also inferior in heat sealing properties and bag-making ability, and were expensive.